The present invention relates to a holographic scanning system for a laser printer.
Conventional laser printer is composed of a laser beam scanning unit which scans a laser beam, a computer which controls the laser beam scanning unit so as to output a laser beam in accordance with the contents to be printed, and a printing unit which forms a picture on a sensitive drum in accordance with the laser beam being applied from the laser beam scanning unit.
Such a conventional type laser printer is illustrated in FIG. 1 and FIG. 2. In the drawings, reference numeral 1 is a laser beam scanning unit, 10 represents a printing unit and 24 represents a computer. The laser beam scanning unit 10 comprises a laser 2 which generates a laser beam, a collimator 3 which converts the laser beam into a parallel beam, a cylindrical lens 4 which focuses the parallel beam passed through the collimator 3 on a rotary polyhedron 5, compensating lenses 7 and 8 which compensate the laser beam reflected by the rotary polyhedron 5 so as to be precisely formed on a drum 11, and a reflective mirror 9 which deflects the laser beams passed through the compensating lenses toward the drum 11.
The rotary polyhedron 5 is rotated by the driven force of a drive motor 6, and each of the compensating lenses 7 and 8 has at least one toric surface.
The printing unit 10 comprises a sensitive drum 11 on which the laser beam which is applied from the laser beam scanning unit 1, is formed, an electrifier 12, a development counter 13, a transfer printer 14, a separator 15, an electricity remover 16, a fixing heater 17, a cleaner 18, and paper feeding, transferring and discharging means. The paper feeding, transferring and discharging means comprise a cassette 19, feeding rolls 20, discharging rolls 21, and a discharging tray 22.
In the drawing, reference numeral 1' is a housing of laser beam scanning unit 1, and 23 represents a paper transferring guide.
In such a conventional laser printer, a laser beam l is generated in accordance with the picture signal from the computer 24 while the laser 2 turns on and off, the laser beam l is converted into a parallel beam by the beam collimator 3 and focused onto the mirror surface of the rotary polyhedron 4 by the cylindrical lens 4.
The laser beam focused on the rotary polyhedron 5 is reflected at various angles according as the rotary polyhedron is rotated by the driving force of the drive motor 6, and scanned toward the direction of arrow in FIG. 2 through the compensating lenses 7 and 8, and then these laser beams are deflected by the reflective mirror 9 and focused onto the drum 11.
In the above, the compensating lenses 7 and 8 are adapted to compensate the focusing locus of the laser beam into a straight line when the laser beam is focused and scanned on the drum 11, and also to compensate the slight movement of the laser beam in the vertical direction by the vibration of the rotary polyhedron 5 during its rotation or when the mirror surface of the rotary polyhedron 5 is tilted.
After the laser beam is formed on the drum 11 as a picture, the printing is carried out by well-known printing process.
However, in such a conventional laser printer, there has been some problems in that since it is difficult to manufacture the toric lenses and cylindrical lenses, the cost becomes high and the productivity becomes low.